Socrates' warning that he will be replaced, and by many, is a curious one. Only a bit earlier, at 31a, he warns the jury not to condemn him, as he will not be easy to replace. Now he suggests that he is quite replaceable, and that the jury will not solve their problem at all by putting him to death. Perhaps we see here that Socrates does indeed change his tactics and his position in order to avoid death. Before he was sentenced, he argued that he was irreplaceable in an attempt to convince the jury not to sentence him. Once he was sentenced, he warned the jury they would only be causing themselves more headaches if they put him to death--perhaps another attempt to get them to change their verdict.
Though it can be supported with textual evidence, this reading is not a desirable one; it would contradict so much of what Socrates has said about not fearing death and maintaining his position that it would drastically weaken the force and integrity of his words. Perhaps a better reading comes from asking what rhetorical effects Plato was aiming for in these two different passages. At 31a, Plato is honoring Socrates, his great mentor, pointing out that he is unique among thinkers, and completely original. Here, at 39c-d, Plato is alluding to himself and many of the other pupils of Socrates who became active after Socrates' death, writing Socratic dialogues and passing on his teachings. Socrates' claim, at 39d, that these new critics will be younger and harsher is borne out by The Apology itself, in which Plato provides a damning criticism of Meletus and the Athenian justice system. Furthermore, the seemingly inconsistent claims at 31a and 39c-d can be reconciled in this reading. Plato is right in saying that Socrates is unique and original: no one like him has appeared in the subsequent two-and-a- half millennia. On the other hand, it is also true that his influence did breed a whole new generation of critics. In fact, Socrates almost single- handedly gave birth to the Western rational philosophical tradition, and if all philosophers that have come since are following in his footsteps, his form of criticism has multiplied exponentially.
Socrates' attitude toward death and the afterlife is fleshed out in far greater detail in Plato's Phaedo, a more mature work that deals primarily with the question of the immortality of the soul. In this dialogue, Socrates' uncertainty is gone, and he is quite convinced that his soul will live on in the afterlife. This contrast between The Apology and the Phaedo is illustrative of the contrast between the early and more mature works of Plato. An early work, The Apology centers more around Socrates' philosophical opinions, which, as he so persistently claims, are agnostic regarding any factual questions. As Plato developed his own voice, he began increasingly to speculate on more metaphysical and epistemological questions, and used Socrates as more of a mouthpiece for putting forward his own views. Thus, in the later Phaedo, we see Socrates claiming to have positive knowledge of what happens after death. As for The Apology, Socrates concludes in typical manner, acknowledging that he does not, and cannot, know for certain what awaits him after death.